There are many types of circuits for providing power to a load. One type of circuit is a rectifier circuit for receiving an alternating current (AC) signal and providing a direct current (DC) output signal. In one application, a ballast circuit for energizing a fluorescent lamp includes a rectifier circuit having an input coupled to an AC power source and a DC output coupled to an inverter circuit. The inverter circuit applies an AC signal to the lamp that is effective to cause a predetermined level of current to flow through the lamp and thereby produce visible light.
Rectifier circuits generally contain one or more rectifying diodes coupled so as to form the input (AC) side and the output (DC) side of the rectifier. Each of the rectifying diodes is conductive for a part of the AC input signal. For example, a first rectifying diode may be conductive for a part of the positive portion of the AC input signal and a second rectifying diode may be conductive for a part of the negative portion. One problem associated with this arrangement is that the diodes which form the rectifier circuit are not operated in a linear manner. Typically, the rectifying diodes are only forward biased, i.e., conductive, when the AC input signal is at or near its peak value. The non-linear operation of the rectifying diodes has a negative impact on the efficiency of the circuit since only a limited amount of power from the AC power source is available to the circuit. Further, the total harmonic distortion (THD) and the Power Factor (PF) of the circuit are also adversely affected.
It would, therefore, be desirable to provide a circuit including a rectifier circuit having rectifying diodes that are operated in a substantially linear manner.